1. Field of the Invention
The present invention relates to a mobile communication system using a mobile terminal device which is capable of accessing both a mobile communication network and a local network simultaneously and a gateway device for relaying between a fixed communication network and a local network.
2. Description of the Related Art
In conjunction with the rapid spread of cellular phones and the Internet, the Internet service using a cellular phone as a terminal has been developed by the mobile communication service providers. This is a service in which a module for processing a communication protocol called TCP/IP used in the Internet is provided in the cellular phone so as to enable WWW service, e-mail delivery, static image and video image data transfer, etc. This service has an advantage in that it becomes possible to freely access not just information closed within the communication service provider but also various information available on the Internet that is spreading worldwide, and for this reason the number of users of this service is increasing rapidly.
Now, the cellular phone Internet service that has an enormous number of users encounters a serious problem regarding how to assign addresses to terminals. Currently, the Internet faces with the problem of IP address shortage in view of the ever increasing number of nodes (routers and terminals), and in the current IPv4, it has been customary to use an address system called private address that is closed within an organization for accesses in an enterprise network and to use global addresses only for accesses to the external of the organization by utilizing the address conversion. Similarly, in the case of the cellular phone Internet service, it is currently customary to use the private address within the cellular phone network by providing an address conversion device (NAT: Network Address Translator) at a border between the IP packet network of the cellular phone company and the global Internet.
On the other hand, the next generation IP specification called IPv6 is currently under the development. The IPv6 can accommodate far more nodes compared with the IPv4 by expanding the IP address from a 32 bits width as used in the IPv4 to a 128 bits width. Similarly, in the case of the cellular phone Internet service, it is possible to assign unique global addresses to all terminals by adopting the IPv6. In this way, communications using a seamless end-to-end connection that does not require a relay device such as NAT on the communication path can be realized by using a wide address space, and it is expected to be advantageous in many aspects including the security and the quality of service (QoS). Also, the IPv6 has a function called address autoconfiguration for automatically generating an address from a network ID managed by each router and a unique ID of the device, and this is expected to make the management of hosts easier.
Also, recently, in conjunction with the advance of the wireless technology, the techniques for locally connecting various types of devices by a wireless network have been developed. One such technique is the wireless standard called Bluetooth which connects devices in short distances by using 2.4 GHz unlicensed radio band. In the Bluetooth, devices can carry out mutual data communications by forming an ad-hoc network called pico-net. The similar network specification also includes the HomeRF which is intended for use in the home network.
Now, using the IPv6 with the above described features, it is possible to consider a situation where a portable terminal is capable of both the Internet access via the cellular phone network and the Internet access via the ISP (Internet Service Provider) network from a home network or a local network such as the Bluetooth or the like. In such a situation, when the portable terminal starts the Internet communications using either the cellular phone network or the local network+the ISP network, the setting of the portable terminal can be made according to commands from a router device on the cellular phone network or a router device on the ISP network. However, in the case where the portable terminal receives a service from the cellular phone network side while it also moves into the local network and carries out communications through the local network, there is a need to determine which one of the Internet access via the cellular phone network and the Internet access via the local network+the ISP network should be selected, and how the setting for it should be made, according to some policy.